An article published in the journal “Astrobiology” reports a study on the possible origin of organic compounds known as thiophenes discovered on Mars by NASA’s Mars Rover Curiosity. Jacob Heinz of the Technische Universität in Berlin and Dirk Schulze-Makuch of Washington State University described some possible processes leading to the formation of thiophenes. These possible processes can be non-biological or biological, and the problem is to find evidence that points to one of them. Thiophenes also exist on Earth and there’s a tendency to think that they’re formed as a result of biological processes, but on Mars this would mean that life forms exist.
On Earth, thiophenes are found in a variety of cases, but always associated with life forms, living and fossil, ranging from white truffles to coal and oil, stromatolites, and microfossils. For this reason we tend to take it for granted that they’re formed by biological processes, but the question becomes much more complicated looking for the origin of thiophenes on Mars. The SAM (Sample Analysis at Mars) instrument, which is actually a suite of three Mars Rover Curiosity instruments, detected thiophenes in sediments analyzed during the mission it’s carrying out in Gale Crater on the red planet, and the two astrobiologists Jacob Heinz and Dirk Schulze-Makuch tried to understand how they were formed.
There are various possible non-biological processes that can lead to the formation of thiophenes on Mars. The two researchers mentioned a possible consequence of meteor impacts and the chemical process known as the thermochemical sulfate reduction, of which the thiophenes are a by-product.
Inevitably, the most intriguing hypotheses concern the possible formation of thiophenes following biological processes because it implies the presence of life forms on Mars, at least in the past. When Mars was young and looked in many ways like Earth there were conditions for the formation of life forms similar to the Earth’s. For example, sulfur-reducing bacteria similar to the ones existing on the Earth could have led to the formation of thiophenes through the process known as bacterial sulphate reduction.
There are several biological processes that lead to the formation of thiophenes and for this reason on Earth we tend to think first of all about them. As for Mars, very solid evidence is needed that one of those processes might have happened on the red planet. A start could come from the analysis of carbon and sulfur isotopes because living organisms alter their ratio in the compounds they produce. Using lighter isotopes requires less energy, so living organisms use mainly those, making it a clue that they’re the product of a biological process.
Some verification regarding thiophenes on Mars could come in the next few years from ESA’s Rosalind Franklin rover. This new rover will be equipped with the Mars Molecule Analyzer (MOMA) instrument, more sophisticated than NASA’s Mars Rover Curiosity analysis instruments. The possibilities of past or present life on Mars has been the subject of discussions for a long time, every new research and every new instrument sent to the red planet can help us come up with an answer.